Fearing that al Qaeda groups in Syria and Yemen are planning to smuggle bombs on European planes bound for the U.S., the Obama administration is urging European authorities to provide increased security at airports on the continent, Reuters reported Wednesday.

It’s unclear whether intelligence picked up on a specific plot or a timeframe for a potential attack.

Bomb makers with the Al Nusra Front, an al Qaeda branch operating in Syria, and Yemen-based al Qaeda in the Arabian Peninsula (AQAP) are believed to be working together in an attempt to make bombs that can’t be detected by current methods at airports, the news wire service reported, citing U.S. national security sources. The bomb specialists may be trying to device non-metallic explosives.

Operatives with Al Nusra and AQAP were believed to have tested new bombs in Syria. One concern is that the groups are going to use militants with Western passports to board passenger planes with the explosives.

The security measures being pushed by the Obama administration include extra checks on electronics and footwear of passengers on U.S.-bound planes, according to Reuters. The administration is also expected to ask for more bomb-detection machines.

AQAP has previously tried using unconventional methods to bomb an airline. Militant Umar Farouk Abdulmutallab smuggled plastic explosives hidden in his underwear aboard a Detroit-bound airliner that took off from Amsterdam but was unsuccessful in detonating the device.